Knowl. Manag. Aquat. Ecosyst. 2017, 418, 25 Knowledge & © R. Rocaspana and E. Aparicio, Published by EDP Sciences 2017 Management of Aquatic DOI: 10.1051/kmae/2017017 Ecosystems www.kmae-journal.org Journal fully supported by Onema SHORT COMMUNICATION Population trends and current status of the endangered Pyrenean sculpin Cottus hispaniolensis in the Spanish part of the Garonne drainage Rafel Rocaspana1 and Enric Aparicio2,* 1 Gesna Estudis Ambientals, Prat de la Riba 51, 25240 Linyola, Catalonia, Spain 2 GRECO, Institute of Aquatic Ecology, University of Girona, 17071 Girona, Catalonia, Spain Abstract – The status of Pyrenean sculpin Cottus hispaniolensis was assessed in the Spanish part of the Garonne drainage on the basis of its distribution and abundance from 2001 to 2016. Population trends showed a progressive reduction in range extension and density, exacerbated by a severe spate occurred in 2013. However, C. hispaniolensis was resilient to this natural disturbance by compensating for mortality with increasing recruitment. Both occurrence and density of Pyrenean sculpin showed a positive correlation with coarse substrates. Riverine habitat deterioration, mainly channelization, presence of dams and flow regulation are the main factors threatening sculpin populations. Several management measures are proposed. Keywords: abundance / catastrophic spate / conservation measures / Cottus hispaniolensis / Garonne Résumé – Tendances et état actuel de la population du chabot pyrénéen menacé Cottus hispaniolensis dans la partie espagnole du bassin de la Garonne. Le statut du chabot pyrénéen Cottus hispaniolensis a été évalué dans la partie espagnole du bassin de la Garonne sur la base des données de distribution et d’abondance au cours de la période 2001-2016. Les tendances de la population ont montré un déclin progressif de l’extension de répartition et de la densité, exacerbé par une crue sévère survenue en 2013. Cependant, C. hispaniolensis a montré une résilience à ce type de perturbation naturelle en compensant la mortalité par un recrutement accru. L’occurrence et la densité du chabot pyrénéen ont montré une corrélation positive avec les substrats grossiers. La détérioration des habitats rivulaires, principalement la canalisation des cours d’eau, la présence de barrages et la régulation des débits, sont les principaux facteurs potentiels qui menacent les populations de chabots. Plusieurs actions de gestion sont proposées. Mots clés : abondance / crue catastrophique / Mesures de conservation / Distribution The sculpins (Cottus sp., Cottidae, Scorpaeniformes) are and brown trout Salmo trutta L. 1758, and the introduced small benthic-dwelling freshwater fish species that occur minnow Phoxinus sp. and Alpine charr Salvelinus umbla mainly in cold, well-oxygenated mountain streams and lakes (L. 1758) are found in a few reservoirs and high mountain lakes (Tomlinson and Perrow, 2003). In Spain, two native sculpin (Aparicio, 2015). Pyrenean sculpin historically occurred in species with a very restricted distribution are found (Doadrio continuous populations located in the main course of the et al., 2011): Adour sculpin Cottus aturi (Freyhof, Kottelat Garonne River and the lower parts of some tributaries and Nolte, 2005) and Pyrenean sculpin Cottus hispaniolensis (de Sostoa et al., 1990; Doadrio et al., 2011). These Bǎcescu and Bǎcescu-Meşter, 1964. The latter is endemic to populations are declining in relation to historical information, the Garonne River basin (south west France and northern but available quantitative data is scarce (Doadrio et al., 2011; Spain) restricted to the southern (upper) part of the drainage in Sousa-Santos et al., 2014). Pyrenean sculpin is currently listed the Pyrenees (Freyhof et al., 2005). as Critically Endangered in the Spanish and Catalan Red Lists The source of the Garonne River is located in the Val of Threatened Species (Doadrio et al., 2011; Aparicio et al., d’Aran (Catalonia, Spain), and flows for ca. 40 km before 2016) and, as Cottus gobio (former synonym), is also included entering to France. Fish assemblages in the Spanish part of the in Annex II of the European Habitats Directive 92/43/EEC. In drainage are almost exclusively composed of Pyrenean sculpin France, there is no available information on its status, and is included as Data Deficient in the French Red List (Keith et al., * Corresponding author: [email protected] 2011). This is an Open Access article distributed under the terms of the Creative Commons Attribution License CC-BY-ND (http://creativecommons.org/licenses/by-nd/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. If you remix, transform, or build upon the material, you may not distribute the modified material. R. Rocaspana and E. Aparicio: Knowl. Manag. Aquat. Ecosyst. 2017, 418, 25 Fig. 1. Map of the Garonne drainage in the Val d’Aran (Catalonia, Spain) and location of the sampling sites (see codes in Tab. 1) showing the distribution area of Pyrenean sculpin Cottus hispaniolensis:(○) indicates sites with fish information data and (●) indicates sites where C. hispaniolensis is positively recorded. Physical barriers (weirs and dams) are marked as lines perpendicular to the river. In June 2013, heavy rain combined with snow melting Fish was sampled from 15 sites during summer and early caused a severe spate in the Garonne River and its tributaries autumn base flow conditions, from 2001 to 2016. Sampling (the estimated return period is 50 years). According to data sites (80–200 m in length) were selected in relation to the from the Bossòst gauging station (42°470100 N; 0°4103200 E), historical range of Pyrenean sculpin, i.e. the main course of flow discharge during the spate exceed 300 m3 sÀ1, whereas the the Garonne River and the lower parts of its main tributaries mean discharge for the 1966–2013 period was 17.3 m3 sÀ1 (Fig. 1). Fish were captured by two pass electrofishing (Ebro Water Authority; http://www.chebro.es/). The cata- (pulsed DC). All captured fish were anaesthetized with clove strophic spate induced dramatic changes in the streams oil, identified to species level, counted, measured (fork length morphology and its consequences produced an additional (FL), mm), weighed (g) and released at the same location concern about the fate of Pyrenean sculpin. The aim of this after recovery. Population sizes (N) of both Pyrenean sculpin ¼ 2ð À ÞÀ1 study was to summarize existing data on the distribution and and brown trout were estimated as N C1 C1 C2 , abundance of Pyrenean sculpin in the Spanish part of the where C1 is the number of fish captured in the first sample and Garonne drainage, and to provide information on the effects of C2 is the number of individuals caught in the second event; À1 the spate of 2013 on their populations. probability of capture was calculated as p =(C1ÀC2)(C1) Page 2 of 5 R. Rocaspana and E. Aparicio: Knowl. Manag. Aquat. Ecosyst. 2017, 418, 25 Table 1. Mean density, density range and percentage of occurrence of Pyrenean sculpin Cottus hispaniolensis in the sampling sites during the period 2001–2016. Information of sampling sites subjected to flow regulation is also included. River Code Regulated N Occurrence (%) Mean density ± SD (ind. haÀ1) Range (ind. haÀ1) Garonne 1 No 5 83 167.8 ± 167.4 0–416.7 Garonne 2 Yes 5 67 41.9 ± 57.1 0–138.9 Garonne 3 Yes 5 100 130.8 ± 111.6 24.4–258.1 Garonne 4 Yes 5 67 49.3 ± 57.3 0–133.3 Garonne 5 Yes 5 67 49.1 ± 54.7 0–111.1 Garonne 6 Yes 5 33 8.9 ± 19.9 0–44.4 Garonne 7 Yes 4 60 14.9 ± 27.1 0–55.6 Ruda 8 No 50 –– Unhola 9 No 50 –– Aiguamòg 10 No 4 60 64.4 ± 106.5 0–222.2 Valarties 11 No 50 –– Nere 12 No 4 60 107.8 ± 135.5 0–281.1 Varradòs 13 No 5 100 288.5 ± 146.2 121.0–500.0 Joeu 14 No 5 83 306.1 ± 388.1 0–925.9 Toran 15 Yes 50 –– (Seber and Le Cren, 1967). Fish density (individuals haÀ1) length-frequency distribution data (Fig. 3) showed a simplified was calculated by dividing estimated number of fish by the structure, dominated by fish from 85 to 135 mm FL, and the 0þ area sampled. Because different sampling efforts were class (<50 mm) was very scarce. The spate occurred in sculpin performed from 2001 to 2013 and not all sites were sampled spawningtime(spring)andcoulddamage the nestsorflush down annually, samples were time pooled as following: 2001–2005, the newly hatched fry (Natsumeda, 2005). In 2015, the 0þ class 2006–2012, 2014, 2015 and 2016. After fish sampling, the was also scarce probably because of a small stock of mature streambed substrate was visually estimated (percentage individuals in the reproductive season. In 2016, 3 years after the composition) and classified according to a modified Went- spate, length frequency distribution showed a substantial worth scale: boulder (particle size >256 mm), cobble (>64– increase in the 0þ class (53.6% of the individuals). These 256 mm), pebble (>16–64 mm), gravel (>2–16 mm), sand results suggest that Pyrenean sculpin populations are resilient to (0.1–2mm)andsilt(<0.1 mm). Percent of the sampled reach severe spates, compensating for mortality with increasing that is pool, riffle, or run habitat was also recorded. Stepwise recruitment in the following years. multiple linear regression was used to test the effect of habitat The linear regression (stepwise procedure, P < 0.05) (substrate composition, channel units, and flow regulation) revealed significant relationships of both sculpin density and biotic (mean brown trout density) predictors on mean and occurrence with substrate composition, explaining the sculpin density and occurrence. The significance level for 78% of the difference in mean density and 72% of the predictor variables was 0.05. Fish densities were log10(x þ 1) difference in percentage of occurrence.